Various types of active headrests have been known, and known active headrests include, for example, those disclosed in Patent Document 1 (JP-A-11-334439), Patent Document 2 (JP-A-2004-9891), Patent Document 3 (JP-A-2000-309242), and Patent Document 4 (JP-A-2000-233713).
An active headrest according to an invention disclosed in Patent Document 1 has a configuration in which the headrest is tilted based on a detection signal from a crash detecting sensor for predicting or detecting a rear crash. It is configured such that an abutting surface (a front part) of the headrest is moved toward a passenger and is also tilted obliquely and upwardly as the headrest is tilted.
An active headrest according to an invention disclosed in Patent Document 2 includes a headrest driving mechanism for advancing the headrest toward the head of a passenger when a crash to the rear of the vehicle is predicted.
An active headrest according to an invention disclosed in Patent Document 3 includes a headrest driving mechanism for moving the headrest up and down, a sensor for detecting the position of the head of a passenger at a surface of the headrest, and elevation adjusting devices for adjusting the elevation of the headrest by operating the headrest driving mechanism based on a detection signal from the sensor.
An active headrest according to an invention disclosed in Patent Document 4 includes a headrest driving mechanism for upwardly moving the headrest toward the head of a passenger when a crash to the rear of the vehicle is predicted.
An invention according to Patent Document 5 (JP-A-2004-122856) is a vehicle passenger protection apparatus, and the passenger protection apparatus includes prediction means for predicting a crash and moving means for moving a vehicle seat to a predetermined position for protecting passenger based on a signal from the prediction means.
Referring to the active headrests disclosed in Patent Documents 1 and 2, the amount of the movement of the headrests upon detection of a crash is always constant regardless of the position of the head of a passenger. Incidentally, the position of the head of a passenger depends on the stature of the passenger and soon. As a result, the active headrests according to Patent Documents 1 and 2 have sometimes been uncomfortable for a passenger because the headrests can push the head of a passenger too much.
Under the circumstance, it is an object of the invention to provide an active headrest which will not over-push the head of a passenger.